This invention relates to electrically-programmable integrated circuit fuses and sensing circuitry for such fuses.
Integrated circuit fuses are used in a variety of applications where configurable circuit elements are needed. For example, fuses may be used to adjust components such as variable resistor and may be used to implement redundancy schemes.
One type of fuse that has been developed uses a polysilicon link capped with a layer of silicide. When a fuse is unprogrammed, most current is conducted through the silicide layer, which has a lower resistance than the polysilicon. A fuse may be programmed by applying a programming current to form an open circuit in the silicide.
The increase in resistance that is produced when a fuse is blown may be sensed by circuitry on the integrated circuit. If the resistance is low, the fuse is considered to be unprogrammed. If the resistance is high, the fuse is considered to be programmed.
If the change in resistance of a fuse during programming is too small, it may be difficult to discern whether a given fuse has been programmed. Higher programming currents may be used to increase the resistance of the programmed fuses, but programming currents cannot be too high without damaging the integrated circuit and wasting power. Moreover, it is important for reliability that the location in the fuse link at which a fuse blows be repeatable.
It would be desirable to provide robust and sensitive integrated circuit fuses.